The invention relates to the telecommunications field, and more particularly to a switching system which is based on a self-routing switch core and having a distributed flow control mechanism.
Patent applications 96480126.0 (IBM Docket FR996040), 96480125.2 (IBM Docket FR996041), 96480117.9 (IBM Docket FR996042), 96480120.3 (IBM docket FR996045) are non-published European applications illustrating a powerful self-routing switch that provides a high switch rate. Flow control mechanisms are essential in switching systems in order to prevent any loss of data. This is particularly true when the switching architecture is based on a switch core and some distributed and remote Switch Core Access Layer (SCAL) elements which may be located in different premises at a distance of over 100 meters. In such systems, it is highly essential that the switch core remain able to slow down the generation of cells coming from one particular SCAL element even if the latter is located in another physical area.
Additionally, as the distance between the different components tend to increase, it is desired that the different flow control signals be transmitted without any further communication wires, which is not particularly easy since the direction of the flow control signals are reverse to that of the normal data flow. This generally prevents the possibility of introducing the control signals for slowing down the generation of cells in the normal data flow conveying those cells.
Finally, the high requirement for sophisticated switching architectures, involving higher speed and higher number for ports of the switching process, tends to favor some complex architectures in the switching techniques, such as the port expansion architecture. Such a system is based on a set of numerous switch cores, connected in a manner which is not easy to achieve, in order to permit the increase in the number of ports of the overall switching architecture. In this situation it is obvious that the flow control mechanism tends to become even more complex and hard to achieve.
The technical problem to be solved by the present invention is to provide an efficient flow control mechanism for a high speed switching architecture, based on a self-routing switch core, even when the different components of the architecture are physically located at different and remote areas.
It is an object of the invention to provide a flow control mechanism that does not require additional control leads or wiring for transporting the different flow control signals for slowing down some components in the switching architecture.
It is a further object to provide an efficient flow control mechanism which operates even when the architecture is based on a port expansion with a great number of individual switching structures in order to provide an aggregate, high speed core having an increased number of input and output ports.
This problem is solved by the process and apparatus in accordance with the present invention, and which is defined in the appended set of claims. The flow control process is particularly well suited for a switching system comprising at least one switch core connected through serial communication links to remote and distributed Protocol Adapters or Protocol Engines through Switch Core Access Layer (SCAL) elements. For each input port i, the SCAL element comprises a receive Protocol Interface (PINT) for the handling of the particular protocol corresponding to the adapter being assigned the input port i and first serializing means for providing the attachment to the switch core by means of first serial communication link(s). When the cells are received in the switch core, they are deserialized by means of first deserializing means. On the other hand, at each output port, the cells are serialized by means of second serializing means and then transmitted via a second serial communication link, such as a coaxial cable or optical fiber, to the appropriate SCAL. When the SCAL receives the cells, they are deserialized by second deserializing means and then transmitted to the Protocol Interface (PINT) circuit for permitting the attachment of the Protocol Adapter.
In accordance with the present invention, the flow control process permits the transmission of two flow control signals, a first Flow Control Receive (FCR) signal flowing from the core to the SCAL, and a second Flow Control Transmit (FCX) signal from the SCAL back to the core. This is achieved without any additional wiring or circuitry even when long distances are involved. To achieve this, the process involves the following steps:
For the transmission of the FCR signal in response to the detection of a local saturation into the switch core, the process causes the transfer of an internal FCR signal to the serializer belonging to the corresponding saturated port. Then the FCR is introduced in the normal data flow to be conveyed through the second serial link to the remote transmit Protocol Interface located in the SCAL which is also the SCAL that includes the receive PINT that generates too many cells for the saturated input port. An internal control signal is then generated to that receive PINT, so that the latter can slow down the production of the cells.
Conversely, when the transmit PINT appears to become saturated, the process permits the transfer of an FCX signal as follows. An internal control signal is generated and locally transmitted to the serializer belonging to the SCAL whose output port is saturated. An FCX control signal is then transmitted in the normal data flow to the switch core and is then decoded by the deserializing means located therein. Once decoded, the FCX signal can be used to inform the core of the saturation that occurred in the transmit PINT.
Particular adaptations are provided when the switching system is arranged in a set of individual switching structures mounted in a port expansion mode. This is particularly achieved with the method as defined in the claims. Thus, there is provided an effective flow control without requiring the use of additional wires or communication links for transmitting the control signals in a direction that is reverse with respect to that of the control flow.